Contribution of STAT3 to Activation of Survivin by Granulocyte-Macrophage Colony-Stimulating Factor in CD34+ Cells.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been shown to specifically stimulate proliferation and differentiation of CD34+ hematopoietic progenitor cells. Although STAT3 was thought to be essential for the transduction of GM-CSF-induced cell proliferation, the downstream signaling mediated by STAT3 to support cell proliferation and growth has not been completely understood. Because the inhibitor of apoptosis protein (IAP) survivin is believed to regulate cell proliferation and survival via its anti-apoptotic function, we chose to study the link between STAT3 signaling and survivin expression in CD34+ cells. We constructed plasmids containing the survivin promoter sequence and performed luciferase reporter assay in CD34+ KG-1 cells stimulated with GM-CSF. These experiments showed that GM-CSF stimulated survivin promoter activity. Chromatin immunoprecipitation (CHIP) and electrophoretic mobility shift assay (EMSA) revealed that STAT3 binds to the core survivin promoter containing a STAT response element (SRE) TT(N)₅AA at sites −264 to −256. Mutation or deletion of this SRE completely abolished the effect of GM-CSF on survivin promoter activity. Furthermore, specific JAK inhibitor and STAT3 siRNA inhibited GM-CSF-induced survivin promoter activity and survivin expression. Inhibition of survivin by STAT3 siRNA or by withdrawal of GM-CSF in a GM-CSF-dependent CD34+ line TF-1 resulted in decreased cell growth and induction of apoptosis. These results suggest that the anti-apoptotic protein survivin is a transcriptional target of STAT3, and that GM-CSF stimulated-CD34+ cell proliferation is regulated by the JAK/STAT3/survivin signaling pathway.